A sensor is a converter used to measure a physical quantity and then convert it into a signal. This signal may be read by an observer or by an electronic instrument. For example, a photodiode may convert the measured light input into a proportional current output, and a deoxyribonucleic acid (DNA) sensor may convert the measured energy of hydrogen bonds into an output voltage. The sensitivity of the sensor represents how much of the output when measuring the physical quantity, and a sensor with higher sensitivity can sense more tiny amount of the physical quantity.